Rick, you've dashed me with the cold reason/logic I needed.
Here, even when I planted out in early May (for several years, a bit later every year) as soon as the last average frost date is past...my tomatoe plants just sat and sullenly shivered and didn't start appreciably growing until after mid-May.
Eventually I was delaying planting out until May 15th: pushing it, as the plants take almost a week to get going.
In conclusion, I realize that I can't change the onset of production earlier for this variety.
No problem: no2w I just need to find a variety that'll do what I want. . . and figure out a way/space to grow iit!
(And I PROMISED myself not to plan to grow any more!